Toner for electrophotography



United States Patent 3,325,409 TONER FOR ELECTROPHOTOGRAPHY Graham C. Whitbread, Norton Summit, South Australia,

Australia, assignor to Research Laboratories of Australia Limited, North Adelaide, South Australia, Australia No Drawing. Filed Aug. 19, 1963, Ser. No. 303,144 Claims priority, application Australia, Aug. 28, 1962,

6 Claims. (Cl. 252-62.1)

This invention relates to electrophotography, and in particular relates to a new and improved liquid dispersible toner suited to the reproduction of line images.

In the past various methods of toner formulation have been proposed for line copy applications such as document copying and plan printing, but the majority of these proposed toners have suffered from serious disadvantages in that they have either been dispersible only in relatively active solvents or have been unstable and thus unsuitable for economic machine operation. Such toners dispersed in aromatic hydrocarbon carrier liquids or halogenated hydrocarbon carrier liquids have also placed serious restrictions on the type of resin used as a binder for Zinc oxide and other particulate photoconductor layers due to solvation of the binder resin during development, with consequent image loss and toner contamination. As it is often desirable to use such relatively solvent sensitive binder resins in particulate photoconductor layers it becomes necessary to provide toners of suitable characteristics for dispersion in carrier solvents to which the binder resin is sufficiently resistant.

We have now found that such preferred binder resins are not seriously affected by immersion of the photoconductor sheet in aliphatic hydrocarbon liquids of KB value less than 28, which liquids are found to have a low aromatic content and a suitable flash point, and it therefore becomes necessary to formulate toners suitable for dispersion in such carrier liquids, the toner particles being of uniform polarity capable of producing high contrast substantially black image deposits, substantially free from pigmentation in non-image or background areas, and scuff resistant when dried.

We have now found that black toners of such properties hereinbefore described, suitable for dispersion in low KB hydrocarbon carrier systems can be formulated using esters of hydrogenated rosins as binders, and that such materials are of uniform polarity and capable of production of substantially black image deposits with little or no background deposit. The degree of scuff resistance attainable can be adjusted by change in the pigment/ resin ratio within the toner and also by the addition of drying oils, such as linseed oil, or by the addition of certain petroleum resins. Such toners have been found to be dispersible in a variety of carrier liquids with KB values as high as 100, but are of particular interest in connection with low KB high boiling point hydrocarbon carrier liquids necessary for development of images on presently preferred binder systems used with particulate photoconductors.

The following examples will serve to illustrate further the principles of this invention.

Example 1 Grams Microlith black CT 20 Microlith blue 4GT 10 Shellsol T 30 The components are mixed together in a high speed stirrer and the resultant cream dispersed in a dispersing fluid in the proportion 0.5-10 grams dispersed phase to 3,325,409 Patented June 13, 1967 100 grams fluid. It should be noted that the Microlith pigments of this example contain approximately percent by weight of a hydrogenated rosin ester. Microlith black CT is carbon black dispersed in hydrogenated rosin ester, and Microlith blue 4GT is phthalocyanine' blue dispersed in hydrogenated rosin ester, The dispersing fluids envisaged in this and following examples are typified by 'Shellsol T, a hydrocarbon petroleum solvent of nil aromatic content manufactured by the Shell Company, boiling range 180-207 C., Flash Point 130 F., KB value 26, specific gravity of 0.761 at 60 F., and by Isopar H, an isoparrafiinic hydrocarbon solvent manufactured by Humble Oil & Refining C0,, boiling range 171-193 C., Flash Point 123 F.., KB value 26.9, and and aniline point of 183 F.; and by Sovasol 35, an isoparafiinc hydrocarbon solvent manufactured by Socony Mobil Oil Co., boiling range 171-199 C., Flash Point 120 C., KB value 26.

The Microlith pigments are manufactured by Ciba Limited, Microlith T series being dispersible in carrier liquids of the desired relatively low solvent power, This toner when used in conjunction with zinc oxide/binder photoconductor layers is capable of producing substantially background free black image deposits which become fairly scuff resistant on drying.

Example 2 The Staybelite ester 10 of Example 2 was replaced by C/ 236 pale glycerol ester, acid value 5-10, melting point 7080 C., manufactured by Grindley & Co. Limited, London.

Example 4 A hydrogenated rosin ester was prepared by heating 100 grams of hydrogenated rosin, such as Staybelite resin, with 400 grams polymerised linseed oil. This varnish was used as a base for the preparation of a toner as follows:

Grams Staybelite varnish Carbon black SRF 35 Victoria blue 5 These components are milled together in a bar mill or triple roll mill and the resultant concentrate dispersed in Isopar H in the proportion 0.5-5 grams concentrate to grams Isopar H. Staybelite resin is a hydrogenated rosin manufactured by Hercules Powder Co. Limited, of the following characteristics, acid value 162, iodine value 135, melting point 70 C., density 1.045 at 20 C.

Example 5 The scuff resistance of toners such as that of Example 3 can be further improved by the incorporation of such resmated pigments as the Microlith T series pigments of Example 1 as follows:

Grams Staybelite varnish of Example 3 85 Microlith black CT 20 Microlith blue 4GT 10 This toner is ground and dispersed for use as in Example 4.

Example 6 The image density of deposited images can be increased to a marked extent without impairment of the scuff resistant properties "by the incorporation of certain petroleum resins such as polyisobutylene in the toner concentrate in addition to the rosin ester. This can be incorporated in a toner such as that of Example 1 as follows:

' Grams Microlith black CT 2O Microlith blue 4GT 10 Polyisobutylene (50% in Sovasol 35) 60 These components are preferably ball milled and dispersed for use in Sovasol 35 in the proportions 0.5-5 grams toner concentrate/100 grams Sovasol 35.

Example 7 The colour value of the toner of Example 2 can be increased by adding in addition 30 grams of a 50% solution of polyisobutylene in Sovasol 35.

What I claim is:

1. A substantially black liquid toner for electrophotographic images consisting essentially of a substantially black pigment material, hydrogenated rosin ester as a binder resin, and a substantially aliphatic hydrocarbon carrier liquid having a KB value less than 28.

2. A toner according to claim 1 wherein the pigment material is predominantly carbon black and the weight ratio of pigment-to-rosin ester is not more than about 1:4.

3. A toner according to claim 2 wherein the carrier liquid is about 100 parts by weight and the pigment and ester together are about 0.5 to 10 parts by Weight.

4. A toner according to claim 1 wherein the ester is 5 selected from the group consisting of the gylcerol ester of hydrogenated rosin and that obtained by heating hydrogenated rosin with polymerized linseed oil.

5. A toner according to claim 4 wherein the pigment material is predominantly carbon black and the Weight ratio of pigment-to-rosin ester is not more than about 1:4. 6. A toner according to claim 5 wherein the carrier liquid is about 100 parts by Weight and the pigment and ester together are about 0.5 to 10 parts by weight.

References Cited LEON D. ROSDOL, Primary Examiner.

JULIUS GREENWALD, Examiner.

I. D. WELSH, Assistant Examiner. 30 

1. A SUBSTANTIALLY BLACK LIQUID TONER FOR ELECTROPHOTOGRAPHIC IMAGES CONSISTING ESSENTIALLY OF A SUBSTANTIALLY BLACK PIGMENT MATERIAL, HYDROGENATED ROSIN ESTER AS A BINDER RESIN, AND A SUBSTANTIALLY ALIPHATIC HYDROCARBON CARRIER LIQUID HAVING A KB VALUE LESS THAN
 28. 